Step-up transformer

ABSTRACT

Open ends of a number of secondary windings are fixed by winding them around a film projection portion formed by cutting and raising insulating films provided between the layers of the secondary windings. This eliminates the requirement that a number of terminals on a bobbin corresponding to the secondary windings be fixed by winding them around the film projection portion, whereby the number of terminals provided on the bobbin can be reduced, and the bobbin can be made smaller in size.

TECHNICAL FIELD

The present invention relates to a step-up transformer which includes aplurality of secondary windings laminated in a plurality of layers withinsulating films therebetween, divided on the basis of a predeterminednumber of turns, and opened at one-side ends thereof and which ispreferable for use, for example, as a high voltage generatingtransformer.

BACKGROUND ART

As a step-up transformer for generating a high voltage for a cathode raytube, there has hitherto been proposed one which includes a plurality ofsecondary windings, for example, eight secondary windings laminated in aplurality of layers, for example, eight layers with insulating filmstherebetween, divided on the basis of a predetermined number of turns,and opened at one-side ends thereof, as shown in FIG. 9.

Referring to FIG. 9, symbol 10 denotes a commercial power source of, forexample, 100 V and 50 Hz. One end and the other end of the commercialpower source 10 are connected respectively to one end and the other endof a rectifying circuit 11 having a diode bridge configuration, apositive output terminal of the rectifying circuit 11 is earthed througha smoothing capacitor 12, and a negative output terminal of therectifying circuit 11 is earthed.

The positive output terminal of the rectifying circuit 11 is connectedto a power source terminal of an oscillation drive circuit 14 through aresistor 13, and the positive output terminal is earthed through aswitching circuit 15 consisting, for example, of a series circuit ofMOS-FET switching devices Q1 and Q2. The switching circuit 15 is sodriven that the switching devices Q1 and Q2 show alternative conductionat a predetermined frequency by the oscillation drive circuit 14.

Furthermore, the switching circuit 15 constitutes a half-bridge circuit,the positive output terminal of the rectifying circuit 11 is connectedto the drain of the switching device Q1, and the source of the switchingdevice Q2 is earthed. In addition, damper diodes D1 and D2 are connectedin parallel to the switching devices Q1 and Q2, respectively.

A connection point between the source of the switching device Q1 and thedrain of the switching device Q2 is earthed through a series circuit ofa resonant capacitor 16, a coil 17, and a primary winding 18 of astep-up transformer T.

The primary winding 18 of the step-up transformer T is supplied with acurrent at a resonance oscillation frequency intrinsic of the seriescircuit.

Symbols 19 a, 19 b . . . 19 h denote eight secondary windings which, asshown in FIG. 11, are laminated on a bobbin 107 with insulating films105 therebetween, are divided on the basis of a predetermined number ofturns, and are opened at one-side ends thereof. Rectifying diodes 20 a,20 b . . . 20 h are each connected, in a vertical row fashion, to apoint between the other-side ends of each adjacent pair of the secondarywindings, of the eight secondary windings 19 a, 19 b . . . 19 h.

Specifically, the diode 20 a is connected to a point between theother-side ends of the secondary windings 19 a and 19 b, the diode 20 bis connected to a point between the other-side ends of the secondarywindings 19 b and 19 c, the diode 20 c is connected to a point betweenthe other-side ends of the secondary windings 19 c and 19 d, the diode20 d is connected to a point between the other-side ends of thesecondary windings 19 d and 19 e, the diode 20 e is connected to a pointbetween the other-side ends of the secondary windings 19 e and 19 f, thediode 20 f is connected to a point between the other-side ends of thesecondary windings 19 f and 19 g, the diode 20 g is connected to a pointbetween the other-side ends of the secondary windings 19 g and 19 h, andthe diode 20 h is connected to a point between the other-side end of thesecondary winding 19 h and the earth.

An equivalent circuit of the secondary winding system constituted of theeight secondary windings 19 a, 19 b . . . 19 h and the eight rectifyingdiodes 20 a, 20 b . . . 20 h is as shown in FIG. 10. By subjecting thevoltages obtained at the secondary windings 19 a, 19 b . . . 19 h tofull-wave double-voltage rectification to produce DC voltages and layingup the DC voltages, it is possible to obtain a high DC voltage, forexample, 32.4 kV. In FIG. 10, capacitors 21 a, 21 b . . . 21 h areinter-layer capacitances of the secondary windings 19 a, 19 b . . . 19h.

In addition, the other-side end of the secondary winding 19 a isconnected to a high-voltage output terminal 23 through a diode 22, and aconnection point between the diode 22 and the high-voltage outputterminal 23 is earthed through a smoothing capacitor 24.

Besides, the high-voltage output terminal 23 is earthed through a seriescircuit of resistors 25 and 26, a detection voltage of a high voltageobtained at a connection point between the resistors 25 and 26 issupplied to a control circuit 27, and the oscillation frequency of theoscillation drive circuit 14 is controlled according to a DC voltageobtained at the high-voltage output terminal 23 by the control circuit27 so that the high DC voltage obtained at the high-voltage outputterminal 23 will be constant.

Meanwhile, a sectional view of an example of the entire constitution ofthe high voltage generating transformer as shown in FIG. 9 is as shownin FIG. 12, in which symbol 101 denotes the secondary winding system. Asshown in FIGS. 11 and 13, the secondary winding system 101 has astructure in which the eight secondary windings 19 a, 19 b . . . 19 h inthe state of being laminated in eight layers with the insulating films105 therebetween are wound around the outer circumferential surface ofthe roughly cylindrical bobbin 107 having walls along both side edges,the insulating films 105 are, for example, belt-like in shape, and thesecondary windings 19 a, 19 b . . . 19 h are so wound as to have a widthslightly smaller than the width of the insulating films 105.

Conventionally, the one-side ends and the other-side ends of the eightsecondary windings 19 a, 19 b . . . 19 h have been fixed by binding themrespectively onto terminals 103 and 104 provided, through terminal bases103 a and 104 a, on one side and the other side of the bobbin 107, andthe diodes 20 and the like have been connected to the terminals 103 and104 to assemble a circuit as shown in FIG. 9.

In addition, as shown in FIG. 12, the secondary winding system 101 isdisposed so as to penetrate through a core 142, which forms a closedmagnetic circuit at the center thereof, together with the bobbin 102 aand a primary winding system 102 constituted of the primary winding 18.

However, when the one-side ends and the other-side ends of the pluralityof windings, for example, the eight windings 19 a, 19 b . . . 19 h arefixed by binding them respectively onto the terminals 103 and 104 as inthe related art, where the number of the secondary windings 19 a, 19 b .. . 19 h connected as required is eight, for example, the numbers of theterminals 103 and 104 provided on the bobbin 107 are each eight, i.e., atotal of 16 terminals are needed, as shown in FIG. 13. Thus, in therelated art, the number of the terminals needed is large, and the bobbin107 is enlarged in size accordingly.

In consideration of the foregoing, it is an object of the presentinvention to make it possible to reduce the number of terminals requiredon a bobbin and to reduce the bobbin in size.

DISCLOSURE OF INVENTION

According to the present invention, there is provided a step-uptransformer including: a primary winding supplied with a switchingvoltage obtained through switching at a predetermined frequency; aplurality of secondary windings for stepping up the switching voltagesupplied to the primary winding which are laminated in a plurality oflayers, are divided on the basis of a predetermined number of turns, andare opened at one-side ends thereof; a bobbin which provides apredetermined spacing between the plurality of secondary windings andthe primary winding and which includes a plurality of terminals forwinding the other-side ends of the plurality of secondary windingstherearound; a core inserted in the bobbin, and excited by the switchingvoltage supplied to the primary winding, to form a closed magneticcircuit; insulating films wound around the bobbin so as to space theplurality of secondary windings from each other by respectivepredetermined thicknesses; rectifying portions provided respectively atthe other-side ends of the plurality of secondary windings, forrectifying stepped-up voltages obtained at the other-side ends of thesecondary windings; and a film projection portion formed by cutting andraising the insulating films, for winding the one-side ends of thesecondary windings therearound.

According to the present invention as above, the open one-side ends ofthe plurality of secondary windings are fixed by winding them around thefilm projection portion formed by cutting and raising the insulatingfilms provided between the layers of the secondary windings. Therefore,the number of the terminals on the bobbin can be reduced, for example,to ½ times the original number in a conventional design, and the bobbincan be reduced in size.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of an example of a secondary winding systemaccording to an embodiment of the step-up transformer of the presentinvention.

FIG. 2 is a partly enlarged perspective view of an example of anessential part of FIG. 1.

FIG. 3 is a partly enlarged perspective view for use in illustratingFIG. 1.

FIG. 4 is a plan view of an example of the secondary winding systemshown in FIG. 1.

FIG. 5 is a partly enlarged perspective view of another example of theessential part of FIG. 1.

FIG. 6 is a partly enlarged perspective view of a further example of theessential part of FIG. 1.

FIG. 7 is a partly enlarged perspective view of yet another example ofthe essential part of FIG. 1.

FIG. 8 is a partly enlarged perspective view of a still further exampleof the essential part of FIG. 1.

FIG. 9 is a circuit diagram showing an example of a step-up transformer.

FIG. 10 is an equivalent circuit diagram of a secondary winding systemof the step-up transformer shown in FIG. 9.

FIG. 11 is a partly enlarged sectional view of an example of thesecondary winding system.

FIG. 12 is a sectional view showing the entire constitution of anexample of a step-up transformer.

FIG. 13 is a plan view of an example of a conventional secondary windingsystem.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the step-up transformer according to the presentinvention will be described below, referring to the drawings.

The present embodiment will also be described referring to an example ofapplication to a step-up transformer circuit as shown in FIG. 9.

Namely, in FIG. 9, symbol 10 denotes a commercial power source of, forexample, 100 V and 50 Hz. One end and the other end of the commercialpower source 10 are connected respectively to one input terminal and theother input terminal of a rectifying circuit 11 having a diode bridgeconfiguration, a positive output terminal of the rectifying circuit 11is earthed through a smoothing capacitor 12, and a negative outputterminal of the rectifying circuit 11 is earthed.

The positive output terminal of the rectifying circuit 11 is connectedto a power source terminal of an oscillation drive circuit 14 through aresistor 13, and the positive output terminal is earthed through aswitching circuit 15 composed of a series circuit of switching devicesQ1 and Q2, for example, field effect transistors (MOS-FETs). Theswitching circuit 15 is so driven that the switching devices Q1 and Q2show alternate conduction at a predetermined frequency by theoscillation drive circuit 14.

Furthermore, the switching circuit 15 constitutes a half-bridge circuit,the positive output terminal of the rectifying circuit 11 is connectedto the drain of the switching device Q1, and the source of the switchingdevice Q2 is earthed. In addition, damper diodes D1 and D2 are connectedin parallel to the switching devices Q1 and Q2, respectively.

A connection point between the source of the switching device Q1 and thedrain of the switching device Q2 is earthed through a series circuit ofa resonant capacitor 16, a coil 17, and a primary winding 18 of astep-up transformer T.

A primary winding 18 of the step-up transformer T is supplied with acurrent at a resonance frequency determined by the resonant capacitor16, the coil 17, and the primary winding 18 of the series circuit.

Incidentally, the primary winding 18 is wound around a bobbin 102 a, asshown in FIG. 12.

Symbols 19 a, 19 b . . . 19 h denote eight secondary windings which arelaminated, with insulating films 105 therebetween, around a bobbin 107,are divided, for example, on the basis of the same number of turns, andare opened at one-side ends thereof. Rectifying diodes 20 a, 20 b . . .20 h are each connected, in a vertical row fashion, to a point betweenthe other-side ends of each pair of the secondary windings, of the eightsecondary windings 19 a, 19 b . . . 19 h.

Specifically, the diode 20 a is connected to a point between theother-side ends of the secondary windings 19 a and 19 b, the diode 20 bis connected to a point between the other-side ends of the secondarywindings 19 b and 19 c, the diode 20 c is connected to a point betweenthe other-side ends of the secondary windings 19 c and 19 d, the diode20 d is connected to a point between the other-side ends of thesecondary windings 19 d and 19 e, the diode 20 e is connected to a pointbetween the other-side ends of the secondary windings 19 e and 19 f, thediode 20 f is connected to a point between the other-side ends of thesecondary windings 19 f and 19 g, the diode 20 g is connected to a pointbetween the other-side ends of the secondary windings 19 g and 19 h, andthe diode 20 h is connected to the other-side end of the secondarywinding 19 h and the earth.

An equivalent circuit of the secondary winding system composed of theeight secondary windings 19 a, 19 b . . . 19 h and the eight rectifyingdiodes 20 a, 20 b . . . 20 h is as shown in FIG. 10. By subjectingvoltages obtained at the secondary windings 19 a, 19 b . . . 19 h tofull-wave double-voltage rectification to produce DC voltages and layingup the DC voltages, it is possible to obtain a high DC voltage, forexample, 32.4 kV. In FIG. 10, capacitors 21 a, 21 b . . . 21 h areinter-layer capacitances of the secondary windings 19 a, 19 b . . . 19h.

In addition, the other-side end of the secondary winding 19 a isconnected to a high-voltage output terminal 23 through a diode 22, and aconnection point between the diode 22 and the high-voltage outputterminal 23 is earthed through a smoothing capacitor 24.

Besides, the high-voltage output terminal 23 is earthed through a seriescircuit of resistors 25 and 26, a detection voltage of a high voltageobtained at a connection point between the resistors 25 and 26 issupplied to a control circuit 27, and the oscillation frequency of theoscillation drive circuit 14 is controlled according to the DC voltageobtained at the high-voltage output terminal 23 by the control circuit27 so that the high DC voltage obtained at the high-voltage outputterminal 23 will be constant.

Meanwhile, a sectional view of an example of the entire constitution ofthe step-up transformer as shown in FIG. 9 is as shown in FIG. 12, inwhich symbol 101 denotes the secondary winding system. As shown in FIGS.1, 4 and 11, the secondary winding system 101 has a structure in whichthe eight secondary windings 19 a, 19 b . . . 19 h in the state of beinglaminated in eight layers with the insulating films 105 therebetween arewound around the outer circumferential surface of the roughlycylindrical bobbin 107 having walls along both side edges, theinsulating films 105 are belt-like in shape, and the secondary windings19 a, 19 b . . . 19 h are so wound as to have a width slightly smallerthan the width of the insulating films 105.

Incidentally, the bobbin 107 is formed by use of, for example, a PPE(polyphenylene ether) resin 1 mm thick, with an epoxy resin injectedthereto, to insulate the primary winding 18 and the secondary windings19 a, 19 b . . . 19 h from each other.

In this embodiment, a film projection portion 109 is formed by cuttingand raising the insulating films 105 at each of both edges of theinsulating films 105 where the windings constituting the secondarywindings 19 a, 19 b . . . 19 h of the secondary winding system 101 shownin FIGS. 1, 2, and 3 are not wound.

The film projection portion 109 is in the form of a strip of paper inthe example shown in FIGS. 1 and 2, and has a right edge portion 111 aand a left edge portion 112 a as both sides along the longitudinaldirection between a tip portion 110 a and a base portion 110 d.

The left edge portion 112 a of the film projection portion 109 isrectilinear in shape, and the film projection portion 109 is in arecessed form (a recessed portion for retaining) at a central portion110 b of the right edge portion 111 a (the side on one side) thereof.

In this embodiment, the open one-side ends of the eight secondarywindings 19 a, 19 b . . . 19 h are wound (bound) around the filmprojection portion 109.

The film projection portion 109 has a structure in which where thecentral portion 110 b is in a recessed form as shown in FIGS. 1 and 2,the width W1 of the tip portion 110 a is greater than the width W2 ofthe central portion 110 b, so that when the one-side ends of thesecondary windings 19 a, 19 b . . . 19 h are wound around the centralportion 110 b, the one-side ends of the secondary windings 19 a, 19 b .. . 19 h thus wound are less liable to be loosened and can be fixedsecurely.

In addition, in this embodiment, as shown in FIG. 3, the other-side endsof the secondary windings 19 a, 19 b . . . 19 h are clamped by the filmprojection portion 109 on the opposite side of the film projectionportion 109 around which the one-side ends are wound, then theother-side ends are fixed by winding them around the terminals 103 or104 of the terminals 103 and 104 provided, through the terminal bases103 a and 104 a, on one side and the other side of the bobbin 107, andthe diodes 20 a, 20 b . . . 20 h and the like are connected thereto, soas thereby to assemble the circuit as shown in FIG. 9.

Besides, as shown in FIG. 12, the secondary winding system 101 isdisposed so as to penetrate through a core 142, which constitutes aclosed magnetic circuit at the center thereof, together with the bobbin102 a and a primary winding system 102 constituted of the primarywinding 18.

According to this embodiment as above, the open one-side ends of theeight secondary windings 19 a, 19 b . . . 19 h are fixed by winding themaround the film projection portion 109 formed by cutting and raisingside portions of the insulating films 105. Therefore, where the numberof the secondary windings 19 a, 19 b . . . 19 h is eight, the number ofthe terminals 103 and 104 provided on the bobbin 107 can be four on eachside, i.e., the number can be eight in total, as shown in FIGS. 1 and 4.Thus, the number of the terminals 103 and 104 to be provided on thebobbin 107 can be reduced to ½ times the ordinary number in theconventional design, and the bobbin 107 can be made smaller in sizeaccordingly.

In addition, FIGS. 5 to 8 show other examples of the film projectionportion 109 of the insulating film 105 around which to wind the one-sideends of the secondary windings 19 a, 19 b . . . 19 h. In the followingdescription of FIGS. 5 to 8, the portions corresponding to those in FIG.2 are denoted by the same symbols as used above, and description of theportions will be omitted.

A film projection portion 109 in the example shown in FIG. 5 is in theform of a strip of paper, and has a right edge portion 111 a and a leftedge portion 112 a as both sides along the longitudinal directionbetween a tip portion 110 a and a base portion 110 d thereof. The rightedge portion 111 a is rectilinear in shape, while the left edge portion112 a is in the form of being recessed at a central portion 110 b.

It will be easily understood that in the example shown in FIG. 5, also,the same function or effect as that in the example shown in FIG. 2 canbe obtained.

A film projection portion 109 in an example shown in FIG. 6 is in theform of a strip of paper, in which a right edge portion 111 a and a leftedge portion 112 a as both sides along the longitudinal directionbetween a tip portion 110 a and a base portion 110 d are in the form ofbeing recessed at a central portion 110 b.

It will be easily understood that in the example shown in FIG. 6, also,the same function or effect as that in the example shown in FIG. 2 canbe obtained.

A film projection portion 109 in an example shown in FIG. 7 is in theform of a strip of paper, and has a right edge portion 111 a and a leftedge portion 112 a as both sides along the longitudinal directionbetween a tip portion 110 a and a base portion 110 d thereof. The widthof the film projection portion 109 gradually decreases as one goes fromthe base portion 110 d toward the tip portion 110 a, and the right andleft edges are most recessed at a portion immediately before the tipportion 110 a; thus, the film projection portion 109 as a whole is inthe form of being recessed at a narrow portion 110 c.

In the example shown in FIG. 7, where one-side ends of secondarywindings 19 a, 19 b . . . 19 h are wound around the film projectionportion 109, the one-side ends of the secondary windings 19 a, 19 b . .. 19 h thus wound are less liable to be loosened and can be fixedsecurely, since the width W1 of the tip portion 110 a is greater thanthe width W2 of the narrow portion 110 c.

A film projection portion 109 in an example shown in FIG. 8 is in theform of a strip of paper, and has a right edge portion 111 a and a leftedge portion 112 a as both sides along the longitudinal directionbetween a tip portion 110 a and a base portion 110 d thereof. The rightedge portion 111 a and the left edge portion 112 a have shapes reverseto those in the example shown in FIG. 7. Therefore, the width of thefilm projection portion 109 decreases as one goes from the base portion110 d toward the tip portion 110 a, and the right and left edges arerecessed most deeply at a portion immediately before the tip portion 110a; thus, the film projection portion 109 as a whole is in the form ofbeing recessed at a narrow portion 110 c.

It will be easily understood that in the example shown in FIG. 8, also,the same function or effect as that in the example shown in FIG. 7 canbe obtained.

While the number of the secondary windings has been eight in the aboveexamples, the number is determined as required according to the highvoltage needed, so that the number naturally may not necessarily beeight.

In addition, the present invention is not limited to the aboveembodiment or examples, and various modifications can naturally beadopted without departure from the gist of the invention.

INDUSTRIAL APPLICABILITY

According to the present invention, open one-side ends of a plurality ofsecondary windings are fixed by winding them around a film projectionportion formed by cutting and raising insulating films provided betweenthe layers of the windings. This ensures that the number of terminalsprovided on a bobbin can be cut down by a number corresponding to thenumber of the windings fixed by winding around the film projectionportion, and the bobbin can be made smaller in size accordingly.

1. A step-up transformer comprising: a primary winding supplied with aswitching voltage that switches at a predetermined frequency; aplurality of secondary windings for stepping up said switching voltagesupplied to said primary winding, wherein said secondary windings arelaminated in a plurality of layers, are divided based on a predeterminednumber of turns, and respectively are opened at first ends thereof; abobbin for providing a predetermined spacing between said plurality ofsecondary windings and said primary winding and including a plurality ofterminals for respectively winding second ends of said plurality ofsecondary windings therearound; a core inserted in said bobbin, excitedby said switching voltage supplied to said primary winding, and forminga closed magnetic circuit; a plurality of insulating films wound aroundsaid bobbin so as to space said plurality of secondary windings fromeach other by respective predetermined thicknesses; rectifying portionsprovided at the second ends of said plurality of secondary windings forrectifying stepped-up voltages obtained at the second ends of saidsecondary windings; and a film projection portion that is formed basedon each of said plurality of insulating films by cutting and raisingsaid insulating films and around which to wind the first ends of saidsecondary windings.
 2. The step-up transformer as set forth in claim 1,wherein said film projection portion comprises a retaining recessedportion for fixing the first ends of said secondary windings by havingthe first ends wound therearound.
 3. The step-up transformer as setforth in claim 1, wherein said film projection portion has a shape inwhich at least one side along a longitudinal direction between a tipportion and a base portion thereof is recessed.
 4. The step-uptransformer as set forth in claim 1, wherein said film projectionportion has a shape in which a width thereof decreases going from saidbase portion toward said tip portion thereof, and the width thereof issmallest at a portion immediately before said tip portion thereof. 5.The step-up transformer as set forth in claim 1, further comprising aresonant capacitor and an inductor connected to said primary winding,whereby said switching voltage supplied to said primary winding has aresonant waveform.
 6. The step-up transformer as set forth in claim 1,wherein said rectifying portions comprise diodes each connected, in avertical row fashion, to a point between the second ends of eachadjacent pair of secondary windings of the plurality of secondarywindings, voltages obtained at said secondary windings are subjected tofull-wave double-voltage rectification to produce DC voltages, and saidDC voltages are summed to obtain a high voltage.
 7. The step-uptransformer as set forth in claim 6, further comprising: switchingdevices for producing said switching voltages; a drive circuit fordriving said switching devices; and a control circuit for controlling afrequency of said drive circuit based on said high voltage.